1. Field of the Invention
The present invention relates to reservoir characterization, and in particular to fracture characterization of hydrocarbon reservoirs to determine petrophysical properties of interest concerning the reservoirs.
2. Description of the Related Art
Fractures in formation rock in subsurface hydrocarbon reservoirs impact the permeability of the reservoir formations. In addition, fractures in non-reservoir intervals affect communication of fluids between reservoirs above and below such intervals, and cause problems in reservoir development and management. Characterizing fractures has been a challenge. So far as is known, fracture characterization has been based on detecting the existence of fractures and attempting to assess their petrophysical properties. Assessment of petrophysical properties has been the most challenging aspect of fracture characterization.
Current methods, so far as is known, have been geometrical based on using borehole imagery or cores to detect and determine the orientation of microfractures. These current methods have been limited to measurements obtained from the borehole wall or a cored section volume. So far as is known, they do not give a direct measure of the impact of fractures on reservoir performance and petrophysics.
U.S. Pat. No. 7,126,340, which issued Oct. 24, 2006, and of which applicant is a named inventor, relates to techniques of characterizing microfractures based on analysis of core samples, also known as plugs, using anisotropy enhanced of magnetic susceptibility. These techniques are based on core samples. As such, the techniques can not be applied to fractures larger than those capable of being encountered in a plug sample. These larger fractures are referred to as meso-fractures or macro-fractures.
In-situ magnetic measurement technologies have so far as is known been limited to measuring natural magnetic polarities and magnetic field intensities in shallow depths in the earth, on the order of hundreds of meters. Thus, in-situ magnetic anisotropy measurements have not been available for characterization of reservoir rock fractures.